1. Field of the Invention
The present invention relates to an anchoring device for a filament body made of fiber reinforced plastic.
2. Description of Related Art
A filament body made of fiber reinforced plastic (composite cable) is one of tendons conventionally used for prestressed concrete. The filament body made of fiber reinforced plastic is a composite material combining carbon fiber, aramid fiber, or glass fiber having high strength, high elasticity, and high heat resistance with epoxy resin, vinylester resin or the like. The filament body made of fiber reinforced plastic has higher corrosion resistance and higher tensile strength than those of a PC steel wire.
It is known, however, that the filament body made of fiber reinforced plastic may be broken when it acts shearing force, local bending, lateral pressure or the like. This presents a problem in which it is difficult to secure the filament body made of fiber reinforced plastic to an anchoring device with a sufficient tensile load maintained. International Publication WO 2011/019075 has disclosed an anchoring structure in which a buffering layer is provided around an anchoring portion of a filament body made of fiber reinforced plastic wedged on an anchoring device. In International Publication WO 2011/019075, the buffering layer reduces shearing force acting on the filament body made of fiber reinforced plastic.
In International Publication WO 2011/019075, a buffer such as a braided net is placed on the filament body made of fiber reinforced plastic wedged into a socket to provide the buffering layer between the filament body made of fiber reinforced plastic which is weak against shearing force and the wedge. The buffering layer distributes (buffers) the shearing force applied by the wedge locally to the filament body made of fiber reinforced plastic to reduce breaks of the filament body made of fiber reinforced plastic at the position of the wedging.
The anchoring structure for the filament body made of fiber reinforced plastic described in International Publication WO 2011/019075, however, does not distribute the shearing force applied by the wedge locally to the filament body made of fiber reinforced plastic. In other words, International Publication WO 2011/019075 provides the structure in which the buffer independent of the anchoring structure distributes the shearing force applied locally to the filament body made of fiber reinforced plastic.
For securing a plurality of tendons, the anchoring device described in International Publication WO 2011/019075 requires a plurality of male members (wedges) and a plurality of female members (sockets) associated with the plurality of tendons. The plurality of tendons is secured through individual wedge effects which apply lateral pressure to the respective tendons.
On the other hand, there is an anchoring structure in which a single anchoring device anchors a plurality of tendons in some of anchoring devices for PC steel wire. The anchoring device is formed of a male member of conical shape and a female member having a conical hollow into which the male member is inserted, and the plurality of tendons are placed at predetermined intervals around a tapered face of each of the male member and the female member. The plurality of tendons is anchored by the male member on the tapered circumferential face of the female member. In the anchoring device, each of the tendons is not secured through independent wedging of the male member and the female member, and the portion for anchoring the tendon is tapered and inclined relative to an axial direction. The anchoring device anchors the tendon by applying lateral pressure from the wedge effect to the tendon along the inclined tapered face. In such an anchoring structure, a higher pressure due to the wedge effect is applied to the tendon than in the anchoring device as described in International Publication WO 2011/019075 in which the lateral pressure is applied perpendicularly to the tendon against a tensile load applied in the axial direction of the anchoring device.
As a result, the anchoring device in which the plurality of tendons are placed at the predetermined intervals in the circumferential direction of the tapered face of each of the single male member and the single female member cannot appropriately anchor the tendons formed of the filament body made of fiber reinforced plastic which is weak against the shearing force and the like than the PC steel wire.